DaveinOlyWA wrote:..the pack is all but submersible and waterproof
The pack is designed to be submersible and waterproof
, as well as impervious to air.
The pack is cooled primarily by conduction, by the metal to metal contact of the module cases and their attachment points on the unibody and case.
It might be useful to think of the LEAF's lower body as a radiator
, which will of course will disperse heat more readily when the temperature differential is higher (lower ambient) and also when there is airflow over the exposed areas.
Remember that the primary thermal management problem in any BEV is in keeping the pack warm enough
in cooler conditions to retain efficiency and capacity. A passively managed pack, as on 2011-18 LEAFs, must be designed for optimum operation in its entire anticipated operating temperature range.
...Besides having an effect on battery life, the battery chemistry also affects the internal impedance of each cell.
As has been noted on this forum, the original Tesla MS/X cell exhibits a significantly greater internal impedance
than the Leaf's. So at the same cell currents, the Tesla cells will develop more heat, increasing the necessity
for TMS for the Tesla versus for the Leaf.
BEV designers take varying (by both kW rate and temperature) rates of impedance into account in designing BEV battery packs and drive-trains.
2011-17 LEAF packs depend on this passive
heat source for their battery heating needs, to keep the pack higher up in the temperature range, giving higher kWh capacity than that available from colder packs.
A major reason for the observable lower efficiency in m/kWh when driving colder temperatures is the greater amount of energy diverted to pack heating, both when charging and discharging, when the pack is colder.
The presumably larger thermal mass of the larger 2018-on LEAF pack(s) should allow them to retain heat longer, a net positive for operating efficiency.
The lower C rate of the larger packs, during both charge and discharge cycles, should also lower the amount of undesirable
heat generated under the relatively unusual conditions (pack temperatures exceeding ~90 F to 100 F) when additional pack heating is undesirable.
So we should expect 2018-on LEAF packs to operate more efficiently and lose capacity at a lower rate than earlier lower kWh packs, even if AESC had made no improvements at all in cell chemistry.
...though, I certainly expect improvements were